Numerous pointing devices for entering commands into a computer are well known in the art. For example, joy sticks, mouses, track balls, and computer pens are commonly used as pointing devices for entering commands into a computer. Many of these devices, such as a mouse and track ball, use a rotatable ball to determine position. Electronic encoders sense rotation of the ball and generate a signal indicative of the ball's rotation to control movement of the cursor on the screen of the computer. Most of these devices include one or more buttons to allow the selection of commands. Typically, a user will use the pointing device to position the cursor on a desired command on the computer display screen, and press a button to select the command. Prior art pointing devices, such as a mouse and a trackball, are not easily usable with a laptop or portable computers because they require a work surface on which to rest the trackball or on which to roll the ball contained within a mouse.
To overcome these problems, a device such as the BallPoint.TM. mouse, described in U.S. patent application Ser. No. 07/425,527, which is commonly assigned with the present invention, attaches to the side of a keyboard to allow pointing and command entry without the requirement of a work surface.
A drawback to pointing devices of the prior art, which was solved by the invention described in the above-referenced patent application, is that the pointing device must be attached in a manner that will prevent damage to the pointing device if excessive pressure is applied to the pointing device. The BallPoint.TM. mouse has release latches that provide a tight mechanical connection between the mouse and the computer, but permit the disconnection of the mouse if excessive pressure is applied. This is particularly useful in situations where a person inadvertently hits the BallPoint.TM. mouse and applies a shearing force to the mouse. The release latches allow the BallPoint.TM. mouse to pop off the computer so as not to damage the device.
A further drawback of prior part devices such as the mouse, the trackball, and the BallPoint.TM. mouse, is the requirement of an external cable coupling the electrical signals between the pointing device and the computer. An electrical cable from the pointing device generally plugs into an interface connector on the computer. The need for an external electrical cable makes the use of such pointing devices cumbersome in an environment such as an airplane or while sitting in a chair with no desk.
Therefore, it can be appreciated that there is a significant need for a pointing device that eliminates the drawbacks of the prior art.